September 29, 2010

Geological Survey identifies new fault zone

The S.C. Department of Natural Resources (DNR) Geological Survey has identified a buried fault zone north of Jamestown in southern Williamsburg and western Georgetown counties. The buried fault was recognized while drilling was being conducted to produce new geology maps under a grant funded by a National Cooperative Geologic Mapping Program STATEMAP program.

The fault zone is marked by buried zones of peat and marsh pluff mud. Carbon dating of peat samples recovered from drill cuttings showed the faulting could have occurred as recently as 16,000 years ago. In geologic terms the fault movement occurred almost yesterday, making it a potential hazard. "More recent movements have not been identified," said Bill Clendenin, State Geologist, "But we can't rule it out."

Renewed earthquake activity along this fault could affect tourism, established infrastructure, new economic development, and natural habitats between Charleston and Myrtle Beach.

Although the primary purpose of the mapping was for land-use planning purposes, an opportunity to investigate potential geologic hazards expanded the scope of the project. Understanding earthquake hazards in the Lower Coastal Plain is considered important because of the 1886 Charleston earthquake.

More than 60 holes were drilled just north of the Santee River Bridge in four sets of closely spaced, north-south lines on side roads parallel Highway 17A to establish an east-west direction of faulting. Drilling results also show that near surface the south side of the fault is down almost 100 feet with respect to the north side, indicating what is referred to by geologists as normal movement.

The fault is thought to be related to the South Georgia rift, a down-faulted zone that developed when the Atlantic Ocean opened and that underlies most of southern South Carolina. The Charleston earthquake has been interpreted to represent renewed faulting of other South Georgia rift fault zones. The Geological Survey will continue to study this fault in the coming year as mapping is expanded eastward toward Georgetown.